This section is intended to introduce various aspects of the art, which may be associated with embodiments of the disclosed techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the disclosed techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Downhole instrumentation in oil and gas wells continues to evolve, with more diverse measurement capabilities being installed in an ever-increasing number of fields. Permanent downhole monitoring (PDM) gauges, measuring pressure and temperature, provide nearly instantaneous signals from the subsurface reservoir. The oil and gas industry have started to collect immense quantities of downhole information, used primarily for reservoir surveillance. This same information provides valuable information about the internal “connectivity” of the reservoir, that is, the ease with which fluids communicate through complex compartments and pathways to reach the borehole. However, interpreting the connectivity signal and separating it from white noise, man-made artifacts, and equipment issues remains challenging. In addition, simple qualitative, often visual, comparisons between producing wells and injector-producer pairs are inadequate to properly characterize the intricate, multi-tiered connectivity inherent to both sandstone and carbonate reservoirs.
The simplest method, and what is commonly done, to determine inter-well connectivity from permanent downhole pressure data is to plot or visually overlay the pressures from different wells versus time and look for dependent pressure behavior. For example, if one well is shut-in, yet the buildup pressures in this well are declining while another well is on production, it may be inferred the wells are in hydraulic communication and thus connected. If the visual technique does not work, the next option is to build a reservoir model and history match individual well bottom hole pressures. The objective is to see if connectivity between wells has to be present for a valid history match, and to estimate the degree of connectivity.
While simple in theory, the visual comparison technique is often difficult to apply in practice because the bottom hole pressures may be affected by many other transient factors such as rate changes and communication from more than one well. Visual inspection may not be able to isolate the subtle or independent impact of another well's production or injection on the permanent downhole pressure record. The history matching technique is time consuming and non-unique.
There is a need for a fast and reliable technique to determine inter-well connectivity from permanent bottom hole pressure data. Wells with permanent down hole gauges are now common (Chorneyko, 2006). The volume of data (up to 1 pressure reading per second being recorded) and the amount of time required for processing (filter, de-noise, and compress) and analysis are factors that limit use of the data. Early and accurate diagnoses of reservoir connectivity will improve the quality and predictability of full-field simulations. The present inventive method fulfills this need and deals with the complicating factors at work.